1. Field of the Invention
The present invention relates to a DC voltage conversion module. The present invention also relates to a semiconductor module provided with a heat dissipation plate, and a method of making such a semiconductor module.
2. Description of the Related Art
Conventionally, switching regulators are widely used in electronic devices as a means for converting a DC input voltage into a DC output voltage corresponding to the target device to which the voltage is to be supplied (see JP-A-2009-278756, for example). FIG. 26 of the present application shows an example of conventional switching regulator. The switching regulator X1 includes a controller 90. Upon receiving an input voltage Vin, the controller 90 generates a pulse voltage corresponding to e.g. an output voltage Vout. By adjusting the pulse width, an appropriate output voltage Vout is obtained.
To convert the pulse voltage outputted from the controller 90 to the DC output voltage Vout, the voltage needs to be smoothed. For this purpose, electronic components such as an input-side capacitor Cin, a coil Lout, an output-side capacitor Cout, a diode Di, resistors R1 and R2 are additionally provided on the upstream and downstream sides of the switching regulator X1. To obtain a proper output voltage, selection and arrangement of these electronic components are important. For instance, when the wiring connecting these electronic components is improperly long, inductance or noise is produced in the wiring itself. In particular, the path length to the ground tends to have a large effect on noise generation. Further, it is desirable that the ESR (equivalent series resistance) is low, because charge and discharge are repeated at the input-side capacitor Cin and the output-side capacitor Cout. When the selection or arrangement of the above-described electronic components is improper, the controller 90 may not be able to fully exhibit its performance.
Meanwhile, various kinds of semiconductor modules incorporating a plurality of semiconductor elements have conventionally been proposed. Such semiconductor elements may include a semiconductor element that generates a relatively large amount of heat (hereinafter referred to as “heating element”). Since the heat emitted by such a heating element may adversely affect on other semiconductor elements, some measures need to be taken. As an example of such measures, it has been proposed to dispose a heat conduction member between the heating element and a heat dissipation plate so that a heat transfer path is formed. For instance, JP-A-2004-87594 discloses a semiconductor module as shown in FIG. 27 of the present application. The semiconductor module X2 includes a substrate 92 on which a plurality of circuit components, including a heating element 91, are mounted. A heat dissipation plate 93 is attached to the substrate 92. The substrate 92 is formed with a wiring pattern 94 on the obverse surface. The heating element 91 is provided with a pair of external electrodes 91a and a ground electrode 91b. Each of the external electrodes 91a is connected to the wiring pattern 94. The ground electrode 91b is formed on the mounting surface of the heating element 91 and held in contact with a heat conduction member 95 filling the through-hole 92a of the substrate 92. The heat conduction member 95 projects from the lower end of the through-hole 92a to be in contact with the heat dissipation plate 93.
For instance, the semiconductor module X2 is made as follows. First, the substrate 92 and the heat dissipation plate 93 are bonded together, and cream solder is applied to the obverse surface of the substrate 92. Thereafter, the substrate 92 and the heat dissipation plate 93 are transferred into a reflow furnace and heated so that the cream solder is melt. In this process, part of the cream solder flows into the space between the substrate 92 and the heat dissipation plate 93 through the through-hole 92a, whereby the heat conduction member 95 as shown in FIG. 27 is formed.
The semiconductor module X2 has the following drawbacks. When the amount of cream solder applied to the substrate 92 is insufficient, the heat conduction member 95 is undesirably separated from the heat dissipation plate 93, so that heat transfer does not occur properly. Conversely, when the amount of cream solder is excessive, undesirable electrical connection may occur between the wirings provided on the reverse surface of the substrate 92.